How similar are endosymbiont strains within the community?
If an ecological community is the primary site of horizontal transfer of
endosymbionts then the same (or very similar) bacterial strains would be
found in multiple host taxa. This would result in a lower estimate of
pairwise divergence among the endosymbionts present. Using the model
from Baldo et al. (2008), we tested whether there is a significant
reduction in the expected pairwise divergence of the endosymbionts found
from the soil arthropod community. Mean pairwise distance was computed
from three different sources: 1) endosymbionts within the community, 2)
their expected value obtained from the equivalent number of pairwise
distances randomly selected from the database, 3) all unique
endosymbiont sequences obtained from PubMLST and NCBI database. These
were computed separately for Wolbachia supergroup A, supergroup
B, Cardinium and Arsenophonus . Results indicate that mean
pairwise distance of Wolbachia supergroup A within the community
(2.67%) was significantly less (Wilcox rank-sum test, p<0.05)
than expected mean (3.54%; Table S4) and mean of all supergroup A
strains in the PubMLST database (3.69%; Figure S6). In contrast, the
mean pairwise distance of Wolbachia supergroup B strains within
the community (4.17%) was significantly more (Wilcox rank-sum test,
p<0.05) than expected mean (3.38%) and mean of B supergroup
strains in the PubMLST database (3.43%). This higher than expected
values for Wolbachia B supergroup strains can indicate presence
of more divergent strains as compared to Wolbachia A supergroup
within this community. However, when all the Wolbachia supergroup
infections were taken together and their mean pairwise distance (8.68%)
was compared with all such strains in the PubMLST database (8.66%), no
significant difference was found (Wilcox rank-sum test,
p>0.05). This perhaps indicates that although the soil
arthropod community yielded several unique Wolbachia infections
(Table 1), on average this still represents a subset of Wolbachiadiversity reported till now. Similar to Wolbachia supergroup A,Cardinium strains also showed similar trend where community
pairwise distance (1.41%) was significantly less (Wilcox rank-sum test,
p<0.05) than expected mean (2.48%) and mean of strains
obtained from the database (2.01%). Whereas mean pairwise distance ofArsenophonus strains within the community (1.19%) was not
significantly different (p>0.05) from the expected mean
(1.38%) as well as from mean of strains obtained from the database
(1.55%). Thus, Wolbachia supergroup A as well asCardinium strains within the community are more closely related
among themselves (Table S4) but not Wolbachia supergroup B andArsenophonus .